As a conventional technology, for example, a high-pressure gas discharge lamp with following structure is disclosed in Japanese Patent Official Gazette laid open No. 2003-187745. The high-pressure gas discharge lamp is provided with a discharge vessel enclosing a discharge space and a light generating substance. The bottom surface of the discharge vessel has a raised first region near an arc formed during lighting, and a second region for storing light generating substance which is moved by the heat during lighting.
In the high-pressure gas discharge lamp mentioned above, the temperature of the bottom surface coolest in the discharge vessel is raised by making the distance between the arc discharge formed during lighting and the bottom surface of the discharge space Shorter. In this situation, temperature balance in the discharge vessel is controlled so well that a high luminous efficiency can be attained and a lighting voltage can also be increased.
A method for manufacturing the above-mentioned high-pressure gas discharge lamp is disclosed in Japanese Patent Official Gazette laid open No. 2003-229058.
However, in the conventional high-pressure gas discharge lamp, the discharge space of the discharge vessel becomes a special and non circular shape due to the structure in which the distance between the arc discharge and the bottom surface of the discharge space is reduced and light generating substance moving by being heated must be accumulated. For this reason, the following problems take place.
First, light generating substance an move rather freely on the bottom surface of the discharge vessel by heat, depositing position or amount of deposition of the light generating substance always fluctuates and is difficult to be fixed at a definite value. Therefore, vaporizing speed etc. of the light generating substance vary widely, and thus an initial rise time of light flax or chroma after lighting of the lamp vary every time the lamp is switched on.
Second, because or the particular shape of the discharge space, convection of vapor of the light generating substance varies complicatedly making the discharge unstable. For this reason, luminance distribution is changed, so that designing of the lighting device becomes difficult.
Third, because the manufacturing of the lamp having a discharge space having such a special shape is difficult, a special manufacturing method should be employed. Further, if the discharge vessel having a little bit deformed from the designed shape is made, fluctuation in lamp characteristics might arise.